1. Field of the Invention
The invention generally relates to a server for providing multimedia information to a network and, more particularly, to techniques for efficiently transmitting a plurality of time-series multimedia applications in a time-division multiplex by controlling the assignment of a CPU (central processing unit) operation time to the transmitted applications.
2. Description of the Prior Art
Applications including video, animation and/or audio are hereinafter referred to as time-series multimedia applications. Compressed multimedia applications may be either transmitted directly as they are (direct transmission), or once stored in a storage device and then transmitted at constant rates (stored transmission).
In the direct transmission, the compressed applications are launched into a network regardless of the transmission band of the network, which may cause the transmission rate to exceed the transmission band variable with time, resulting in the destruction of transmitted data. For this reason, the direction transmission is possible only when the network transmission band is sufficiently higher than the transmission rate, in which there is no need of the present invention.
A transmission scheme of stored multimedia at a constant rate is described in "Video server software--Video Network File System," IEICE (The Institute of Electronics, Information and Communication Engineers) trans. Vol. J-77-A, No. 9, pp. 1-8. In this system, stored applications are read out and transmitted at a constant rate. This system reads out a frame of data for each of stored applications to be transmitted for transmission. Assuming that two applications AP1 and AP2 are to be transmitted and that both the frame size of the two applications are 10 Kbps, if the applications AP1 and AP2 are to be transmitted at rates of 10 Kbps and 5 Kbps, respectively, then the system transmits one AP1 frame per second and one AP2 frame per two seconds. In this way, each application is transmitted at a constant rate as long as the total load on the CPU does not exceeds the processing capacity of the CPU and the total transmission rate dose not exceeds the transmission bandwidth of the network. However, These conditions are not always satisfied.
It is therefore an object of the invention to provide a method and a system which are used when actually measured transmission rates of a plurality of multimedia applications differ from required transmission rates for the applications and which are for allocating time slices of the CPU to the threads for transmitting the multimedia applications such that the applications are transmitted at the required transmission rate.
A reduction in the transmission rate of a thread causes a delay of transmission by the thread resulting in asynchronism among transmitted applications.
It is another object of the invention to provide a method of and a system for temporarily changing the allocation of the available time slices to the threads so as to resolve the a synchronism among transmitted applications.
It is another object of the invention to provide a method and a system which are used when the number of time slices available to the threads has decreased to be insufficient to transmit the applications to be transmitted and which adjust the allocation of the available time slices to the threads according to the priorities of the applications.